The present invention relates to lost-circulation materials and, more particularly, in one or more exemplary embodiments, to methods and compositions that utilize lost-circulation materials comprising composite particulates.
Cement compositions are commonly utilized in subterranean methods, particularly subterranean well construction, completion, and remedial methods. For example, in subterranean well construction, a pipe string (e.g., casing and liners) may be run into a well bore and cemented in place. The process of cementing the pipe string in place is commonly referred to as “primary cementing.” In a typical primary cementing method, a cement composition may be pumped into an annulus between the walls of the well bore and the exterior surface of the pipe string disposed therein. The cement composition sets in the annular space, thereby forming an annular sheath of hardened, substantially impermeable cement that supports and positions the pipe string in the well bore and bonds the exterior surface of the pipe string to the subterranean formation. Among other things, the annular sheath of set cement surrounding the pipe string functions to prevent the migration of fluids in the annulus, as well as protecting the pipe string from corrosion. Cement compositions also may be used in remedial cementing methods, such as in squeeze cementing and the placement of cement plugs.
In addition to cement compositions, drilling fluids are also used in subterranean methods. During the drilling of a well bore in a subterranean formation, a drilling fluid may be used to, among other things, cool the drill bit, lubricate the rotating drill string to prevent it from sticking to the walls of the well bore, prevent blowouts by serving as a hydrostatic head to counteract the sudden entrance into the well bore of high pressure formation fluids, and/or remove drill cuttings from the well bore. A drilling fluid may be circulated downwardly through a drill pipe and drill bit and then upwardly through the well bore to the surface. A variety of drilling fluids may be used during the drilling of well bores into a subterranean formation. For instance, the drilling fluid used may be any number of fluids (gaseous or liquid) and mixtures of fluids and solids (such as solid suspensions, mixtures, and emulsions).
One problem associated with subterranean methods may be the undesirable loss of at least a portion of the fluid (e.g., cement composition, drilling fluid, etc.) into the subterranean formation penetrated by the well bore. This problem may be referred to as “lost circulation” and the sections of the formation into which the fluid is lost may be referred to as “lost-circulation zones.” A variety of factors may contribute to lost circulation. For example, subterranean formations traversed by well bores may be weak, highly permeable, and/or fractured. In some instances, the formations may be unable to withstand the hydrostatic pressure normally associated with the fluid being introduced into the well bore. For example, the hydrostatic pressure may be sufficient to breakdown the formation, thereby allowing the fluid to be lost into the formation. Furthermore, the hydrostatic pressure may be sufficient to force the fluid into natural or created fractures and/or permeable zones of the formation, resulting in loss of the fluid into the formation. The loss of the fluid may be undesirable for a number of reasons. For example, premature dehydration of a cement composition may occur due to loss of fluid from the composition into the formation, potentially leading to excessive viscosity and even potential termination of cementing. In addition to drilling fluids and cement compositions, problems with lost circulation may also be encountered with other fluids, such as completions fluids (e.g., completion brines), workover fluids and spacer fluids, that may be introduced into a well bore.
A number of methods have been employed to control lost circulation. One method involves the introduction of a settable composition into a lost-circulation zone to seal the zone, preventing and/or reducing the flow of the fluid into the zone. However, this method will typically require an undesired interruption in the subterranean method. Another method commonly involves contacting the lost-circulation zone with lost-circulation materials in an attempt to plug off and/or bridge fractures and/or permeable zones in the formation where the cement composition may be lost. To contact the lost-circulation zone, the lost-circulation materials may be included in the fluid that is introduced into the well bore. Examples of lost-circulation materials include ground coal, petroleum coke, sized calcium carbonate, asphaltenes, perlite, cellophane, plastic materials, ground oyster shells, ground nut hulls, flakes, fibers (e.g., polypropylene- or zirconium-coated glass fibers), and ground thermoset polymer laminates, such as laminates of paper or fabric with melamine resin.